Silicon single crystal wafers are widely used for manufacture of semiconductor devices. As the silicon single crystal wafers, wafers whose front surface is a (100) crystal plane are often used. As to such a silicon single crystal wafer, since a front side of a wafer has a cleaving direction or characteristics at the time of manufacturing a semiconductor device which are equal to counterparts of a back side of the same, even if the front side and the back side of the wafer are countercharged in a process of manufacturing silicon single crystal wafers from a single-crystal ingot of silicon, no problem arises. (However, the above may not be applicable when different treatments have been applied to the front side and the back side of the wafer, respectively).
On the other hand, Patent Literature 1 discloses a need for making a determination on wafer front and back sides of each silicon single crystal wafer sliced off with an off-angle so that slicing is performed from a specific lattice plane at a slant at the time of slicing a single-crystal ingot.
Further, to determine a front side and a back side of the silicon single-crystal wafer, there is also disclosed a method for determining the front and back by applying an X-ray from an X-ray source having a relative position fixed to the silicon single crystal wafer, detecting a diffracted X-ray from a crystal plane with an off-angle by a detector having a relative position fixed to the silicon single crystal wafer, and comparing an output from the detector with a predetermined threshold value.